As they look about them, infants routinely observe many different physical events: for example, they may see a parent pour juice into a cup, stack dishes on a table, or store groceries in a cupboard. Over the past 10 years, my collaborators and I have been working on developing an account of how infants reason about simple physical events, and how this reasoning becomes gradually more sophisticated with experience. In the Progress Report, I summarize the results of 15 projects conducted during the last grant period that helped us test and extend our account. As a result of this research, we now have a much clearer idea of how infants' physical-reasoning system operates: what specific information infants are likely to represent when watching a physical event, and how they are likely to use this information to interpret and predict the event's outcome. Over the past few years, we have also begun to explore how infants who do not spontaneously represent key information about an event may be induced to do so through various contextual manipulations. Some of these effects appear to depend on subtle interplays between the physical-reasoning system and two other systems suggested by findings in the adult and infant visual cognition literature: the object-tracking system and another system my collaborators and I term the object-representation system. This is a truly exciting era in the field of infant cognition, as developments in different subfields are coming together to paint a much more detailed picture of the computational architecture that underlies infants' responses to objects and events. The first project in the next grant period (PROJECT 1) will continue our investigation of the physical-reasoning system, and will attempt to shed light on striking findings from the last grant period having to do with event category effects and dcalages in infants' acquisition of their physical knowledge. The other projects (PROJECTS 2-11) will explore possible links between the physical- reasoning system and the two other systems mentioned above. In particular, these projects should shed light on how infants respond not only to single events, but also to sequences of events involving the same or different objects. In all, 11 projects (comprising 30 experiments) are planned that will allow us to dramatically expand our understanding of infants' physical reasoning, and to establish new and productive connections to other subfields of infant cognition. As in the previous grant period, the projects will use violation-of-expectation and action tasks. In addition, we are in the process of developing one additional method anticipatory-looking tasks that should provide further converging evidence for our conclusions. Project Narrative During the first year of life, infants normally acquire a great deal of knowledge about the physical world. How do they do so? The present research will help shed light on the cognitive architecture that allows infants, from a very early age, to represent, to reason, and to learn about physical events.